Stringed instruments such as guitars are known in which the bridge is mounted so that by manual operation of a "trem bar", the bridge can be pivoted about an axis transverse to the strings during playing, thereby to vary the tension on all strings simultaneously; the result is a controlled variation of the pitch of all strings, whereby distinctive sound effects, such as a wavering pitch known as tremolo can be produced, as an example. In a full-dumping guitar the tension of the strings can be completely relieved by pivoting the bridge, which is known as full-dumping.
One way in which this has been accomplished has been to mount a pivotable bridge in an opening extending completely through the guitar, along with adjustable springs mounted in the rear of the recess and accessible from the rear, which springs urge the bridge in the direction to tighten the springs; typically the pivoting torque exerted on the bridge by the springs just balances the oppositely-directed torque exerted by the strings, so that the bridge "floats" in a balanced equilibrium position when no disturbing external force is applied, from which position it can be pivoted in either direction by a lever or "trem bar" extending outward from the front face of the instrument, thereby to produce the desired manually-controlled variation in pitch of all strings. In order to maintain the desired balance, i.e. the appropriate spring tension to counteract the string tension, the guitar is provided with a rear cover which is removed so adjustment of spring tensions can be made from the rear side of the instrument.
In addition, the bridge structure is typically of one piece with its underlying support, and therefore causes difficulties in changing the bridge itself, making it difficult for example to substitute a wooden string-engaging bridge for a metal or plastic one, or vice versa.
It is therefore desirable, among other things, to provide a stringed instrument of the tremolo type in which adjustment of the springs and replacement of the bridge are easier, manufacture of the entire instrument is easier and less expensive, and the tonal quality of the instrument is not compromised by requiring use of a covered opening in the back of the guitar.